1. Field of the Invention
The present invention pertains to an insufflation system and method, as well as an insufflation attachment for a ventilation system, that delivers a flow of insufflation gas to the airway of a patient to remove expired gases from a patient""s anatomical dead space and/or the structural dead space in a breathing circuit during ventilation, and, in particular, to an insufflation system, method, and attachment in a ventilation system that delivers a flow of insufflation gas to the patient""s airway in such a manner so as to minimize stagnation pressure in the patient""s lungs due to the flow of insufflation gas into the patient and to an insufflation system, method and attachment that can be used in conjunction with a conventional ventilation system without altering the operation of the conventional ventilation system.
2. Description of the Related Art
It is known to reduce rebreathing of exhaled gases in an intubated patient or in a patient with a tracheostomy by providing a flow of insufflation gas, such as oxygen, an oxygen mixture, or other therapeutic gas, into the distal end of the patient""s breathing circuit. FIG. 1 illustrates an example of such a conventional system, commonly referred to as a tracheal gas insufflation (TGI) system, in which a flow of insufflation gas is delivered to the airway of the patient. A primary flow of breathing gas that augments or completely supports the patient""s breathing is delivered using a conventional ventilator.
As shown in FIG. 1, an endotracheal tube 30 inserted into an airway 32 of a patient 34 through the oral cavity delivers the primary flow of breathing gas from a ventilator 36 to the patient""s lungs 38. In such a conventional ventilation system, a breathing circuit 40 delivers the primary flow of breathing gas from the ventilator to the patient via a first limb 42, and exhaled gas from the patient is removed via a second limb 44. First and second limbs 42 and 44 are typically flexible tubes coupled to endotracheal tube 30 via a coupling member, such as a Y-adapter. For purposes of this invention, the breathing circuit includes all of the structures associated with the ventilation system that communicate the primary flow of breathing gas with the airway of the patient, such as first limb 42, second limb 44, endotracheal tube 30 and any coupling members.
As the patient inspires, the primary flow of breathing gas is delivered by ventilator 36 to the patient""s respiratory system, i.e., the airway and lungs, via breathing circuit 40. Typically, the primary flow of gas delivered to the patient by the ventilator is controlled based on the total volume delivered, the pressure of the gas delivered, or the patient""s respiratory effort, the latter of which is known as proportional assist ventilation (PAV). While an endotracheal tube, which is passed into the patient""s airway via the oral cavity, is illustrated in FIG. 1 as being part of the breathing circuit, it is to be understood that other methods for delivering and/or interfacing breathing gas to the patient, such as a tracheostomy tube, nasal and/or oral mask, or an nasal intubated endotracheal tube, are commonly used in conventional ventilation systems as part of the breathing circuit.
As the patient expires, i.e., breathes out, the exhaled gas, which is laden with CO2, is removed from the lungs and airway via endotracheal tube 30 and second limb 44 of breathing circuit 40. Typically, an exhaust valve (not shown) associated with second limb 44 and operating under the control of ventilator 36 manages the flow of exhaust gas from the patient so that, if desired, a certain level of positive endexpiratory pressure (PEEP) can be maintained in the patient""s respiratory system. In some ventilation systems, the second limb includes an exhaust valve that is controlled by the ventilator but is not contained within the ventilator itself.
It can be appreciated that at the end of exhalation, not all of the exhaled gas containing CO2, for example, is exhausted to atmosphere. A certain amount of exhaled gas remains in the physiological and anatomical dead space within the patient and in the structural dead space within the breathing circuit. The structural dead space in the breathing circuit is the portion of the breathing circuit beginning at a distal end 55 of endotracheal tube 30 or tracheostomy tube to a location 46, where the exhalation (second) limb 44 separates from the rest of the breathing circuit. It is generally desirable to prevent the exhaled, CO2 laden gas in this dead space from being rebreathed by the patient, so that the patient receives the maximum amount of oxygen or other therapeutic gas and a minimal amount of CO2 during each breath. In some patients, such as patients with cranial injuries, it is imperative that their CO2 level not be elevated.
Tracheal gas insufflation (TGI) is one method that attempts to remove the exhaled gas from the physiological, anatomical and structural dead spaces in a patient being treated with a ventilator. Tracheal gas insufflation involves introducing an insufflation gas, such as oxygen, an oxygen mixture, or other therapeutic gas, into the patient""s airway 32 at the distal end of breathing circuit 40. In the embodiment illustrated in FIG. 1, an insufflation gas source 48, such as a pressurized tank or oxygen or an oxygen wall supply, delivers a flow of insufflation gas via a conduit 50 as a stream of gas into the patient""s airway. Conduit 50 is also referred to as an xe2x80x9cinsufflation catheter.xe2x80x9d In a conventional TGI system, a proximal end of conduit 50 is coupled to insufflation gas source 48 through a control valve 52, and a distal end of conduit 50 is located generally within or near the distal end of endotracheal tube 30 so that the flow of insufflation gas is directed toward lungs 38, as indicated by arrow 54. Typically, the distal end of conduit 50 is located just above the patient""s carina. The oxygen rich flow of insufflation gas discharged from the distal end of conduit 50 displaces the exhaled air in the anatomical and structural dead spaces so that the patient inhales the fresh (non CO2 laden) gas on the next breath, thereby minimizing rebreathing of CO2 to keep the patient""s CO2 levels as low a possible.
Conventionally, there are two techniques for delivering the flow of tracheal insufflation gas to a patient. According to a first TGI technique, the flow of insufflation gas is delivered to the patient continuously during the entire breathing cycle while the ventilator delivers the primary flow of breathing gas to the patient. This technique is commonly referred to as a xe2x80x9ccontinuous TGI system.xe2x80x9d This continuous TGI delivery method, however, has a significant drawback in that conventional ventilators are not capable of accounting for the additional volume of gas delivered to the patient by the continuous TGI system. As a result, the extra volume of gas bled into the breathing circuit by the continuous TGI system is simply summed with the prescribed volume of gas being delivered by the ventilator. A possible outcome is that an excessive pressure of gas is delivered to the patient, possibly over-inflating the patient""s lungs. This excessive pressure is referred to as xe2x80x9cautoPEEP.xe2x80x9d A disadvantage associated with autoPEEP is that it increases the patient""s work of breathing, because in order to initiate inspiration, the patient must generate an inhalation force that is strong enough to overcome the autoPEEP pressure. AutoPEEP may also cause tissue damage due to the hyper-inflation of the patient""s lungs.
These problems are dealt with, at least in part, in conventional continuous TGI systems by carefully adjusting the ventilator settings to avoid over-inflation. It can be appreciated that xe2x80x9cfoolingxe2x80x9d the ventilator so that the continuous flow of insufflation gas does not over-inflate the patient""s respiratory system is not an ideal solution because it does not maximize the operating abilities of the ventilator. The ventilator must be specifically configured to deal with this extra insufflation gas, rather than being configured as it normally would in the absence of the flow of insufflation gas. On the other hand, maximizing the operating characteristics of the ventilator by setting it up without accounting for the flow of insufflation gas may result in excessive CO2 levels in the patient or hyperinflation of the patient. In addition, adjusting the operating characteristics of the ventilator to prevent over-inflation when a continuous TGI system is used requires a highly trained operator to make the correct fine-tuning adjustments to the ventilator. Furthermore, this continuous TGI technique requires constant monitoring of the patient and ventilator system because changes in the patient""s breathing cycle that may require reconfiguring of the ventilator or the continuous TGI system can occur in very short time periods.
According to a second TGI technique, referred to as a xe2x80x9cphasic TGI system,xe2x80x9d the flow of insufflation gas is controlled so that the insufflation flow is only delivered to the patient during the expiratory phase, preferably at the end, while the exhaust valve associated with the second limb of the breathing circuit is open. Because the exhaust valve is open when the flow of insufflation gas is delivered, the extra volume of insufflation gas being delivered to the patient displaces an equal volume of gas out of the breathing circuit through the exhaust port and, therefore, does not over-inflate the patient""s lungs. This phasic approach, however, requires a relatively complicated control mechanism for controlling the flow of insufflation gas in conduit 50, for example, by controlling valve 52 using ventilator 36, to ensure that the flow of insufflation gas is only delivered while the exhaust valve associated with second limb 44 is open. It can be appreciated that this phasic TGI technique increases the complexity and cost of the ventilation system and the TGI system due to the precise timing required to control the operation of the ventilator and valve 52, so that the gas is delivered at the correct time during the patient""s breathing cycle.
Another drawback associated with conventional TGI systems, including both the continuous and phasic TGI techniques, is that autoPEEP is also caused by a phenomenon known as stagnation pressure. Stagnation pressure, also known as dynamic pressure, is the pressure or force generated when a flowing gas is brought to rest by isentropic flow against a pressure gradient. The magnitude of the stagnation pressure is proportional to the square of the change in velocity of the gas. Because the insufflation gas in a conventional TGI system is directed into the patient""s airway using a relatively small diameter tubing, typically 0.1 inch diameter, it has a relatively high velocity, which is decelerated into a closed volume, namely the patient""s airway and lungs. As a result, a stagnation pressure is created within the patient, thereby exacerbating the autoPEEP problem. It should be noted that the problem of autoPEEP due to stagnation pressure is prevalent in both the continuous and phasic TGI systems because the timing at which the flow of insufflation gas is introduced into the patient does not affect the magnitude of the stagnation pressure generated.
Accordingly, it is an object of the present invention to provide a tracheal gas insufflation system for introducing a flow of insufflation gas into the airway of a patient that overcomes the shortcomings of conventional TGI techniques. This object is achieved according to one embodiment of the present invention by providing a TGI system that includes an insufflation catheter having a proximal end portion that is located generally outside a patient and a distal end portion that is located in an airway of a patient during use. The insufflation catheter provides the flow of insufflation gas to the patient. A vent assembly is provided at the distal end portion of the insufflation catheter. The vent assembly has first and a second port that discharges the flow of insufflation gas from the insufflation catheter. It can be appreciated that a vector force will be associated with the discharge of the flow of insufflation gas from each port of the vent assembly.
A first port in the vent assembly directs a first portion of the flow of insufflation gas from the insufflation catheter generally in a first direction into the patient""s respiratory system. In addition, a second port directs a second portion of the flow of insufflation gas generally in a second direction out of the patient""s respiratory system. The vent assembly is configured and arranged such that a net of all second vector force components associated with the flow of insufflation gas in the second direction is greater than a net of all first vector force components in the first direction responsive to the flow of insufflation gas exiting the venting means. As in a conventional TGI system, providing the flow of insufflation gas in the first direction generates a positive stagnation pressure. However, providing the flow of insufflation gas in the second direction generates a negative stagnation pressure within the patient. The present inventors discovered that a pressure drop occurs in the patient or in the patient circuit as a result of the insufflation catheter being placed in the patient, which tends to increase the positive stagnation pressure. Therefore, the flow of insufflation gas in the second direction should be increased above that in the first direction to counteract the pressure drop in the patient circuit. This ensures that the negative stagnation pressure offsets out the positive stagnation pressure, so that substantially no stagnation pressure or autoPEEP is generated within the patient.
The present invention also contemplates directing the flow of insufflation gas from the insufflation catheter in a variety of directions and locating the distal end of the insufflation catheter in a variety of locations, so long as the net vector force of the expelled gas from the vent assembly is sufficiently low so as to avoid creating a problematic stagnation pressure in the patient.
In a second embodiment of the present invention, instead of the vent assembly with two ports, two insufflation catheters are provided to accomplish the same function. The distal end of a first insufflation catheter directs the flow of insufflation gas in the first direction generally toward the patient""s lung. The flow in the second direction, generally opposite the first direction to provide a balancing of the positive and negative pressures created by the flow of insufflation gas, is provided by a second insufflation catheter. Of course, this balancing of pressures may require providing a larger flow of insufflation gas in the second direction to overcome the pressure drop induced by the presence of the insufflation catheter or catheters in patient. The distal end of the second insufflation catheter is configured and arranged such that, in an operative position, it directs the flow of insufflation gas in the second direction, away from the lungs. The flow of gas in the first and second insufflation catheters is provided substantially the same so that the combination of flows from these catheters performs the same function as the bi-directional vent discussed above, i.e., the net vector forces resulting from the introduction of insufflation gas into the patient""s airway at the distal end of the first and second insufflation catheter combination is substantially zero, thereby minimizing the creation of a stagnation pressure or autoPEEP in the patient.
It is a further object of the present invention to provide an insufflation system that does not create significant positive stagnation pressures within the patient and that can be used in a conventional ventilation system to provide a flow of insufflation gas into the patient""s airway. This object is achieved by providing an insufflation system as described in either of the preceding paragraphs and that further includes an exhaust valve disposed at a portion of the breathing circuit outside the patient. The exhaust valve is configured and arranged to exhaust gas from the breathing circuit to ambient atmosphere at an exhaust flow rate that that is substantially the same as the flow rate at which the insufflation gas is introduced into the breathing circuit by the TGI system. The flow of insufflation gas into the patient and discharge of exhaust gas to ambient atmosphere are provided irrespective of the primary flow of breathing gas to the. The result of this balance between the amount of gas introduced to the breathing circuit and the amount of gas exhausted from the breathing circuit is that there is no net increase or decrease in the amount of gas in the breathing circuit. Therefore, no special modification of the ventilator or its operation is needed.
This equalization of the flow of gas into and out of the patient""s breathing circuit provided by the TGI system is accomplished in one embodiment of the present invention by continuously exhausting gas from the breathing circuit over a range of pressures within the breathing circuit while the flow of insufflation gas is also continuously introduced into the patient. As a result, gas is continuously exhausted from the breathing circuit preferably at the same rate the flow of insufflation gas is introduced into that circuit.
It is yet another object of the present invention to provide a system for supplying a therapeutic gas to a patient in which a flow of insufflation gas is introduced into the patient""s airway without over inflating the patient and without any modification of the operation of the gas flow generator, which provides a primary flow of breathing gas to the patient, to account for the excess gas introduced into the breathing circuit. This object is achieved by providing a system for supplying therapeutic gas to a patient that includes a first tube that inserts into a patient""s airway for providing a primary flow of breathing gas to the patient. An insufflation catheter generally disposed in the first tube provides a flow of insufflation gas to the patient at a first flow rate. An exhaust valve is coupled to the first tube and is configured and arranged to exhaust gas from the first tube to ambient atmosphere at a second flow rate that is substantially the same as the first flow rate. The flow of insufflation gas into the patient and the discharge of exhaust gas to ambient atmosphere are provided irrespective of the primary flow of breathing gas to the patient. In one embodiment of the present invention, the exhaust valve continuously exhausts gas from the first tube to ambient atmosphere at the second flow rate despite pressure variations within the first tube.
It is still another object of the present invention to provide an insufflation attachment for use with a conventional ventilation system, which provides a primary flow of breathing gas to the patient. The insufflation attachment is used to introduce a flow of insufflation gas into the airway of the patient in a manner that overcomes the shortcomings of conventional insufflation techniques. According to the principles of the present invention, this object is achieved by providing an insufflation attachment that includes a first tube adapted to be coupled in a breathing circuit. The proximal end of an insufflation catheter is coupled to the first tube. The insufflation catheter is configured and arranged such that a distal end portion thereof is generally disposed in an endotracheal or tracheostomy tube when the first tube is coupled to the breathing circuit. A vent assembly is provided at the distal end of the insufflation catheter. The vent assembly has at least one port that discharges the flow of insufflation gas from the insufflation catheter. The vent assembly includes a first port that directs a first portion of the flow of insufflation gas from the insufflation catheter generally in a first direction into the patient""s respiratory system. In addition, a second port directs a second portion of the flow of insufflation gas generally in a second direction out of the patient""s respiratory system. The vent assembly is configured and arranged such that a net of all vector force components in the first direction and in the second direction resulting from the discharge of insufflation gas into the patient""s airway via the vent assembly is substantially zero. As noted above, the positive stagnation pressure created by the flow of insufflation gas in the first direction is offset by the negative stagnation pressure created by the flow of insufflation gas in the second direction so that substantially no stagnation pressure is generated within the patient.
In an alternative embodiment, instead of the vent with two ports, two insufflation catheters are employed. The distal end of a first insufflation catheter directs the flow of insufflation gas only in the first direction toward the patient""s lung, thereby simplifying the configuration for this catheter. The opposing flow in the second direction opposite the first direction is provided by a second insufflation catheter also coupled to the first tube. More specifically, the distal end of the second insufflation catheter is configured and arranged such that, in an operative position, it directs the flow of insufflation gas in the second direction, so that the net vector forces associated with the flow of insufflation gas from the first and second insufflation catheters are substantially zero or so that a greater flow is provided in the second direction to provide additional negative stagnation pressure that offsets the pressure drop induced by the resece of the insufflation catheter in the breathing circuit.
It is a further object of the present invention to provide an insufflation attachment that avoids autoPEEP due to a stagnation pressure and that can be used in a conventional ventilation system in which a flow of insufflation gas is continuously introduced into the patient""s airway. This object is achieved by providing an insufflation attachment as described in either of the immediately preceding paragraphs and further comprising an exhaust valve coupled to the first tube. The exhaust valve is configured and arranged to exhaust gas from the first tube, i.e., the breathing circuit, such that the flow rate for the exhaust gas exiting the breathing circuit is substantially the same as the flow rate for the insufflation gas introduced into the breathing circuit by the TGI system. The flow of insufflation gas into the patient and the discharge of exhaust gas to ambient atmosphere are provided irrespective of the primary flow of breathing gas to the patient. The result of this balance between the amount of gas introduced to the breathing circuit and the amount of gas exhausted from the breathing circuit irrespective of the primary flow of breathing is that there is no net increase or decrease in the amount of gas in the breathing circuit. Therefore, the ventilator does not xe2x80x9cseexe2x80x9d the introduction of the insufflation gas into the breathing circuit so that no special modification of the ventilator or its operation are needed. In one embodiment of the present invention, exhausting gas from the breathing circuit is done continuously over a range of pressures within the breathing circuit at a flow rate that matches the flow rate of the insufflation gas. As a result, there is substantially no net accumulation of gas in the breathing circuit due to the introduction of insufflation gas into the breathing circuit.
It is yet another object of the present invention to provide an insufflation method that overcomes the shortcomings of conventional TGI techniques. This object is achieved by providing a TGI method that includes the steps of delivering a flow of insufflation gas to the airway of a patient and directing the flow of insufflation gas such that a net of all vector force components in a first direction generally into the patient""s respiratory system and in a second direction generally out of the patient""s respiratory system resulting from discharging the insufflation gas into the patient""s airway is substantially zero. In one embodiment, this is accomplished by directing a first portion of the flow on insufflation gas in a first direction generally toward the patient""s lungs and directing a second portion in a second direction generally opposite the first direction to minimize or eliminate the generation of stagnation pressure in the patient. As noted above, the present invention also contemplates providing a greater flow of gas in the second direction than is provided in the first direction to overcome the additional pressure drop imposed by the presence of the insufflation catheter in the system.
It is a further object of the present invention to provide an insufflation method that overcomes the shortcomings of conventional insufflation techniques in which a flow of insufflation gas is delivered to the airway of patient in addition to the primary flow of breathing gas. This object is achieved by providing a method that includes the steps of (1) delivering the primary flow of breathing gas to the airway of the patient via a breathing circuit, (2) delivering a flow of insufflation gas to the airway of a patient at a first flow rate, and (3) exhausting gas from the breathing circuit to ambient atmosphere at a second flow rate that is substantially the same as the first flow rate. The flow of insufflation gas into the patient and the discharge of exhaust gas to ambient atmosphere are provided irrespective of the primary flow of breathing gas to the patient. In a further embodiment of the present invention, the exhaust valve continuously exhausts gas from the breathing circuit to ambient atmosphere at the second flow rate over a range of pressures within the breathing circuit.
These and other objects, features, and characteristics of the present invention, as well as the methods of operation and functions of the related elements of structure and the combination of parts and economies of manufacture, will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only and are not intended as a definition of the limits of the invention.